Twelve days after two young Iowa cousins vanished, the mother of one of the girls is asking authorities -- and her family -- to move on from their focus on her.

Misty Cook-Morrissey said a state agent asked during Monday's polygraph whether she had anything to do with the abduction of her daughter, 10-year-old Lyric Cook-Morrissey, and niece, 8-year-old Elizabeth Collins. She said she was asked whether she knows where they are and if she could take investigators to them, adding she answered "no" to all those questions.

The polygraph was the second test authorities had her take.

"It went well," Cook-Morrissey told The Associated Press in a phone interview. "They can rule me out of their book and move on to something else."

The polygraph came a week after authorities said Cook-Morrissey and her husband weren't cooperating. In a news briefing on Monday, Black Hawk County Chief Deputy Rick Abben declined comment on Cook-Morrissey's polygraph test but said investigators were getting better cooperation from her and her husband. 

The girls were last seen heading out on a bike ride on July 13 in Evansdale, a town of 4,700 in northeast Iowa. After combing the area and draining a nearby lake, authorities announced they felt the disappearance was an abduction, and said on Saturday they thought the girls were still alive.

Both Cook-Morrissey and her husband have spent time in prison on drug charges, NBC's John Yang reported Tuesday on TODAY, but Cook-Morrissey she said that had nothing to do with the girls' disappearance.

Elizabeth's mom, Heather Collins, said her relationship with her sister, Cook-Morrissey, has been splintering amid investigators' recent statements that Cook-Morrissey wasn't fully cooperative.

"Even though we would like to be as one family, it has made it to be two separate families," Heather Collins said of her sister, Misty, Lyric's mom.

There is a $50,000 reward for the girls' safe return. FBI spokeswoman Sandy Breault said Monday that investigators want to interview a person who was paddleboating on the lake around the time the girls disappeared. She said that person, who has not voluntarily come forward, could help investigators learn what happened to the girls but was not considered a suspect.

The Associated Press contributed to this report.

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